May Luk on mon 16 jan 06
Dear David and friends;
Thank you very much for the email.
How odd that you mention your oil spots glaze. I had the impression that
I was working on your glaze last year in my informal glaze group. I have
these test tiles next to my computer for a whole year! It was the
tenmoku challenge spear-headed by John Britt and he gave us -
generously, as always - a whole load of high iron recipes. One of them
was called Bailey Oil Spot. We all thought it was a Mike Bailey glaze
which had travelled to the U.S. and then came back to us in the U.K.
Somehow we associated Bailey with yourself because you two collaborated
on glaze technology and write in Ceramic Reviews together often. You'll
be pleased to know your name came up when we were discussing the test
results, though it was a mis-understanding. I have checked, and it
wasn't your glaze. There might be another Bailey from the U.S., I don't
know, come to think of it :-)
The Oil Spot was hard for us. We had fired 6 recipes in 4 different
kilns, we only have one minor success. The spots were so small, we need
magnifying glass to see them. The rest are mostly lumpy chocolate
puddings. Now that I have re-read your notes. I can see that we were
stingy with our firing ramps coming down. It's difficult to play with
long firing ramps just for a few test tiles in a load. We are always
aware of carbon footprints, and the cost of firing, in our group. W
Another factor that we didn't try very hard was being urban potters, we
are just not very keen on brown glaze. :-) It was a good learning
experience, nevertheless. We learnt a lot about Iron Oxides.
I would like to take this opportunity to thank *you* and everybody else
who had written long and detail notes on glaze / science / materials /
calculations and share them with others. I am most grateful to the long
and detailed private emails I received from my virtual clayart friends.
I think that's true generosity. It was in this spirit that I started my
informal glaze group locally. Just a way to glaze it forward.
Warmest Regards
May
London, UK
David Hewitt wrote:
The following is what I give in my reply. As you will
> see I ask to know how the recipient gets on with it. Sadly to say I
> rarely hear anything more, so I presume that it has not worked for them.
>
> David
>
> OIL SPOT
> You are very welcome to have the recipe, but I would ask that you will
> acknowledge its origin if you do use it or put it on your web site.
> Also, if you try it, I would appreciate knowing how you get on with it.
> Transporting glazes is not always straight forward as I have indicated
> on that particular page of my web site. Also, please note that the
> application of the glaze and the firing can make all the difference
> between a mediocre and a good result. My procedures are given below in
> some detail.
>
> Oil Spot recipe ref:- HAE8
>
> Nepheline Syenite 150
> China clay 350
> Whiting 80
> Talc 80
> Quartz 340
> Red Iron Oxide 80
> ____
> 1080
>
> I do not think that any of these materials should present too much of a
> problem for you. My analysis of his recipe is:-
>
> K2O .04 Al2O3 .98 SiO2 6.15
> Na2O .14 Fe2O3 .29
> CaO .46
> MgO .36
>
> Apply the glaze fairly thickly. Fire at least to cone 9 well down in
> oxidation and soak for at least 30 minutes. I also fire down by reducing
> the temperature by 20 oC and holding for 15 minutes and repeating this
> down two more steps. You need to give the 'spots' time to develop. Some
> tendency for pin holing on outside / underneath surfaces of bowls if you
> do not soak or fire down long enough. If you find at first that the
> surface oil spots have not smoothed out, re-fire the pots. They won't
> run. Precise firing will no doubt depend on your particular kiln, its
> size, rate of temperature climb and cooling at top temperature etc., but
> I am sure you will know about all this and the differences you can get
> between one kiln and another. The firing is important to produce good
> oil spots. The results I have shown have been produced in a small
> electric kiln, a Cromartie CTL75 on Potclays 1149 porcelain.
| |
|
